#include <stdio.h>
#include <unistd.h>

int main() {
    FILE* pf = fopen("log.txt", "a");
    if (pf == NULL) {
        perror("fopen:");
        return 1;
    }
    fprintf(pf, "hello linux:% d\n", 100);
    fclose(pf);
    return 0;
}
